My 82 XJ650 4K0 is misfiring and wont run..Help...

Hi all.
Am new here so go asey as we say in Ireland.
I got me hands on a beautiful 1982 XJ650 4KO model.
She has only 22k genuine miles and I know the original lady owner...
Problem is...the bike was a non runner before I bought her. Problem with the carbs I was told. So the carbs were cleaned by ultrasound and she ran like a dream.
160 miles later on she started to misfire got progressively worse and now wont start at all.
So I removed the tank and flushed her out, cleaned the fuel tap put fresh petrol in and replaced the coils at the same time. Perfect spark at all four leads and still wont start..All I get is a small stream of whiteish smoke from the exhaust (its a 4 into 1) and when I let go the starter button she lets a little backfire.
Is it possible that because the tank wasnt flushed at the same time the carbs were cleaned that I will have to go to the hassle of cleaning them all over again or could it be something else.?
I appreciate andy help you guys can offer.
Cheers.
Morg.

 

could certainly be the carbs if you are getting good spark on all 4. Did you put an inline fuel filter on? That would have kept the junk out of the carbs.

Also is the smoke white or gray? Could be oil. What's your compression like?

 

Yes, it's possible that the carbs have gotten filled back up with crud if you didn't install an inline fuel filter.

When were the valves last checked? If never, you're at the mileage where it will start to have an effect.

Do a compression test, let's see what that tells us.

 

Go ahead and take the carbs back off and clean them again. You won't need to break the rack apart, just remove the bowls and clean the jets and float needles. Pay close attantion to the pilot jets, those little holes get plugged easily. Do a bench sync and install a fuel filter. Just like the others have said, compression test and valve adjustment check.

 

Thanks to all of you guys..
Funny thing is though she didnt smoke at all prior to this happening. I would imagine at 22k the engine is still very fresh. She was never thrashed or abused so i wouldnt expect her to be burning oil..Is it possible that the whiteish smoke is junk in the carbs being burnt off.?

 

Is it smoke, or unburned fuel vapor? That's white too. Got a smell to it?

 

You said when you let go of the button it backfires.

This was tickling something in my head. I just remembered.

In a car that can be a sign of a bad ignition module or ignition switch but since the bike's ignition and starter button are separate, doesn't apply here.

It does sound possible that it is overfueling, and can't spark hard enough to fire in that rich environment until just as you let go of the starter. It's common to these bikes for the starter to pull a lotta juice away from the coils. So you get a real strong spark cycle just as you let off the starter, when the motor is still spinning down.

In real cold weather, when it's cranking slow, I know mine will not start while cranking...I have to catch it just as I let go of the starter, give the throttle a blip right at that moment and it fires up....or floods. I'm talking serious cold, like temps sane people don't ride in.

But the upshot is, it sounds like you are seeing a lot of unburnt fuel. I think you were flooding, and it finally soaked the plugs too wet to run.

Pull a plug and verify, I bet it soaking wet with gas. Check your battery, and charging volts once you get it started. Eliminate that.

Wet plugs, throw a new set in, it won't ever start again otherwise. Then work from there...carb work if it starts wet fouling those...

 

Thanks dude.
thankfully it doesnt get that insanely cold here in Ireland although last winter was the coldest in 50 years.
I put a new set of coils in her at the same time I flushed the tank. Charged up the battery. Plenty of juice in her.
Havent checked the plugs yet though. When I first rode her home she ran like a dream and I cant understand how she acted up so quiclky in the space of 160 miles.
Any reason why she would overfuel.? There is no obvious sign of a petrol smell off her. Or like an eejit did I possibly flood her.? When I first had her which is only a few months ago she started first touch of the button without choke.
Thanks again.
Morg.

 

Pull a couple of plugs, see what you got. Until then, if's just speculation.

Check your coil connections.

Even at best, it seems these bikes are walking a line between firing right up and not having enough juice to spark when cranking...don't assume, verify.

If the charging system is not up to snuff, that could be the whole explanation here.

I don't rule out any basics as being known factors until verified...saved a lot of tail-chasing in the shop...

 

You could have gotten a small piece of junk trapped above one or more needles and then they didn't shut off the fuel supply and it overflowed. Check your oil level and smell the fill hole. If it smells like gas and the oil is overful change it and the filter. Reclean the carbs, verfiy float level with cler tube method, replace the plugs and install an inline filter. Put fresh fuel in and give it a go. I'd bet she starts.

 

This to me says too rich to begin with. I'm more and more suspecting flooding here...if you're talking cold start, first one of the day.